I want to generate logistic regression equation based on coefficient estimates. I am trying to find automate solution -
The coefficient estimates are stored in a dataset. They look like below -
Variables | Estimate |
Intercept | 0.001 |
ABCD | 0.558356 |
DEFG | 0.464783 |
HIJKL | 0.111268 |
MNOP | 0.811915 |
score = 0.001 + 0.558356 * ABCD + 0.464783 * DEFG + 0.111269 * HIJKL + 0.811915 * MNOP
p = 1 / (1 + exp(-score))
I want the following equation to be stored in a separate data set. In this data set, there would be a single column named "Equation" and first row contains the equation:
P_1 = 1 / (1 + exp( -(0.001 + 0.558356 * ABCD + 0.464783 * DEFG + 0.111269 * HIJKL + 0.811915 * MNOP))
Note : I am aware of SCORE, OUTMODEL and INMODEL statements in PROC LOGISTIC to calculate predicted probability. But my task is to note down the equation based on estimates.
Build the string using CAT_ functions:
data want;
length eq $200;
do until (done);
set estimates end=done;
if Variable = "Intercept" then
eq = catx(" + ", Eq, Estimate);
else
eq = catx(" + ", Eq, catx(" * ", Estimate, Variable));
end;
Eq = cats( "P_1 = 1 / (1 + exp( -(", Eq, "))");
keep Eq;
run;
PG
Build the string using CAT_ functions:
data want;
length eq $200;
do until (done);
set estimates end=done;
if Variable = "Intercept" then
eq = catx(" + ", Eq, Estimate);
else
eq = catx(" + ", Eq, catx(" * ", Estimate, Variable));
end;
Eq = cats( "P_1 = 1 / (1 + exp( -(", Eq, "))");
keep Eq;
run;
PG
Thanks a ton. It works like charm. Could you please explain how it works -
if Variable = "Intercept" then
eq = catx(" + ", Eq, Estimate);
else
eq = catx(" + ", Eq, catx(" * ", Estimate, Variable));
end;
CATX function concatenates values (strings or formatted numbers) and adds the first function argument (e.g. " + ") between the concatenated values. So here, the string eq is built up by adding to it ( eq = catx(" + ", eq, something) ) the intercept estimate or the concatenation of the estimate and the variable name, separated by " * ", using the CATX function again. Initially, eq is empty.
Read the manual for more fun details about the CATX, CATS, and CATT functions .
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